Information on the fetal and perinatal metabolism of man, particularly during the last half of gestation and of the newborn is understandably scarce. Studies on the rhesus fetus (M. mulatta), which is biologically similar to the human primate, are therefore invaluable. The overall purpose of our studies is to acquire information on the metabolic control mechanisms and the interrelations of carbohydrate, lipid, and amino acid metabolism especially oxidation in the rapidly growing (fetal and neonatal) and adult muscle of rhesus monkeys. We will use several approaches to identify rate-limiting enzymes in cardiac, diaphragm, and voluntary skeletal muscle of fetuses from 50% of term to birth and of adult muscle. For example, 1) mass-action ratios will be determined in situ and compared with the apparent equilibrium constant; the effects of altered glycolytic flux rates on the intracellular contents of relevant metabolic intermediates and cofactors will also be investigated; 2) the rate of lactate-C14 production from various precursors in glycolysis such as fructose-6-P-C14 and fructose-1,6-diP-C14 will be compared in a muscle extract; 3) the effects of 3',5'-cyclic AMP (cAMP), ATP, citrate, Pi, and other effector molecules on the production of lactate-C14 will be studied and the results compared with those on a purified phosphofructokinase (PFK) enzyme. Since the cAMP level is closely linked to the control of many rate-limiting enzymes such as PFK, we will study cAMP levels and the kinetics of adenyl cyclase in adult and fetal muscle and will ascertain how early in gestation they are affected by prostaglandins. In view of the recent interest in cyclic 3',5'-guanosine monophosphate (cGMP), its level and the kinetics of the enzyme guanylcyclase will also be investigated in muscles at different stages of development. Since levels of cyclic nucleotides are also determined by the rate of degradation, we will also study the kinetics of cAMP and cGMP phosphodiesterases of fetal muscle. Finally, we will complete our investigation of amino acid oxidation by skeletal muscle fiber groups from fetal and adult rhesus monkeys.